package org.prashant.sqlduniya.sqlmanager.util;

/*
 * RandomGUID
 * @version 1.2 01/29/02
 * @author Marc A. Mnich
 *
 * From www.JavaExchange.com, Open Software licensing
 *
 * 01/29/02 -- Bug fix: Improper seeding of nonsecure Random object
 *             caused duplicate GUIDs to be produced.  Random object
 *             is now only created once per JVM.
 * 01/19/02 -- Modified random seeding and added new constructor
 *             to allow secure random feature.
 * 01/14/02 -- Added random function seeding with JVM run time
 *
 */
import java.net.*;
import java.util.*;
import java.security.*;

/*
 * In the multitude of java GUID generators, I found none that
 * guaranteed randomness.  GUIDs are guaranteed to be globally unique
 * by using ethernet MACs, IP addresses, time elements, and sequential
 * numbers.  GUIDs are not expected to be random and most often are
 * easy/possible to guess given a sample from a given generator.
 * SQL Server, for example generates GUID that are unique but
 * sequencial within a given instance.
 *
 * GUIDs can be used as security devices to hide things such as
 * files within a filesystem where listings are unavailable (e.g. files
 * that are served up from a Web server with indexing turned off).
 * This may be desireable in cases where standard authentication is not
 * appropriate. In this scenario, the RandomGUIDs are used as directories.
 * Another example is the use of GUIDs for primary keys in a database
 * where you want to ensure that the keys are secret.  Random GUIDs can
 * then be used in a URL to prevent hackers (or users) from accessing
 * records by guessing or simply by incrementing sequential numbers.
 *
 * There are many other possiblities of using GUIDs in the realm of
 * security and encryption where the element of randomness is important.
 * This class was written for these purposes but can also be used as a
 * general purpose GUID generator as well.
 *
 * RandomGUID generates truly random GUIDs by using the system's
 * IP address (name/IP), system time in milliseconds (as an integer),
 * and a very large random number joined together in a single String
 * that is passed through an MD5 hash.  The IP address and system time
 * make the MD5 seed globally unique and the random number guarantees
 * that the generated GUIDs will have no discernable pattern and
 * cannot be guessed given any number of previously generated GUIDs.
 * It is generally not possible to access the seed information (IP, time,
 * random number) from the resulting GUIDs as the MD5 hash algorithm
 * provides one way encryption.
 *
 * ----> Security of RandomGUID: <-----
 * RandomGUID can be called one of two ways -- with the basic java Random
 * number generator or a cryptographically strong random generator
 * (SecureRandom).  The choice is offered because the secure random
 * generator takes about 3.5 times longer to generate its random numbers
 * and this performance hit may not be worth the added security
 * especially considering the basic generator is seeded with a
 * cryptographically strong random seed.
 *
 * Seeding the basic generator in this way effectively decouples
 * the random numbers from the time component making it virtually impossible
 * to predict the random number component even if one had absolute knowledge
 * of the System time.  Thanks to Ashutosh Narhari for the suggestion
 * of using the static method to prime the basic random generator.
 *
 * Using the secure random option, this class compies with the statistical
 * random number generator tests specified in FIPS 140-2, Security
 * Requirements for Cryptographic Modules, secition 4.9.1.
 *
 * I converted all the pieces of the seed to a String before handing
 * it over to the MD5 hash so that you could print it out to make
 * sure it contains the data you expect to see and to give a nice
 * warm fuzzy.  If you need better performance, you may want to stick
 * to byte[] arrays.
 *
 * I believe that it is important that the algorithm for
 * generating random GUIDs be open for inspection and modification.
 * This class is free for all uses.
 *
 *
 * - Marc
 *
 * Revised by: Mahmoud Parsian
 */
public class RandomGUID extends Object {

    public String valueBeforeMD5 = "";
    public String valueAfterMD5 = "";

    private static Random myRand;
    private static SecureRandom mySecureRand;

    /*
     * Static block to take care of one time secureRandom seed.
     * It takes a few seconds to initialize SecureRandom.  You might
     * want to consider removing this static block or replacing
     * it with a "time since first loaded" seed to reduce this time.
     * This block will run only once per JVM instance.
     */

    static {
		mySecureRand = new SecureRandom();
		long secureInitializer = mySecureRand.nextLong();
		myRand = new Random(secureInitializer);
    }


    /*
     * Default constructor.  With no specification of security option,
     * this constructor defaults to lower security, high performance.
     */
    public RandomGUID() {
		getRandomGUID(false);
    }

    /*
     * Constructor with security option.  Setting secure true
     * enables each random number generated to be cryptographically
     * strong.  Secure false defaults to the standard Random function seeded
     * with a single cryptographically strong random number.
     */
    public RandomGUID(boolean secure) {
		getRandomGUID(secure);
    }

    /*
     * Method to generate the random GUID
     */
    private void getRandomGUID(boolean secure) {
	MessageDigest md5=null;
	StringBuffer sbValueBeforeMD5 = new StringBuffer();

	try {
	    md5 = MessageDigest.getInstance("MD5");
	} catch (NoSuchAlgorithmException e) {
	    System.out.println("Error: " + e);
	}

	try {
	    InetAddress id = InetAddress.getLocalHost();
	    long time = System.currentTimeMillis();
	    long rand = 0;

	    if(secure) {
		rand = mySecureRand.nextLong();
	    } else {
		rand = myRand.nextLong();
	    }

	    // This StringBuffer can be a long as you need; the MD5
	    // hash will always return 128 bits.  You can change
	    // the seed to include anything you want here.
	    // You could even stream a file through the MD5 making
	    // the odds of guessing it at least as great as that
	    // of guessing the contents of the file!
	    sbValueBeforeMD5.append(id.toString());
	    sbValueBeforeMD5.append(":");
	    sbValueBeforeMD5.append(Long.toString(time));
	    sbValueBeforeMD5.append(":");
	    sbValueBeforeMD5.append(Long.toString(rand));

	    valueBeforeMD5 = sbValueBeforeMD5.toString();
	    md5.update(valueBeforeMD5.getBytes());

	    byte [] array =  md5.digest();
	    StringBuffer sb = new StringBuffer();
	    for(int j=0; j<array.length;++j) {
		int b = array[j]&0xFF;
		if(b<0x10) sb.append('0');
		sb.append(Integer.toHexString(b));
	    }

	    valueAfterMD5 = sb.toString();

	} catch (UnknownHostException e) {
	    System.out.println("Error:" + e);
	}
    }


    /*
     * Convert to the standard format for GUID
     * (Useful for SQL Server UniqueIdentifiers, etc.)
     * Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
     */
    public String toString() {
	String raw = valueAfterMD5.toUpperCase();
	StringBuffer sb = new StringBuffer();
	sb.append(raw.substring(0,8));
	sb.append("-");
	sb.append(raw.substring(8,12));
	sb.append("-");
	sb.append(raw.substring(12,16));
	sb.append("-");
	sb.append(raw.substring(16,20));
	sb.append("-");
	sb.append(raw.substring(20));

	return sb.toString();
    }


	public static String getGUID() {
		RandomGUID myGUID = new RandomGUID();
		//System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
		//System.out.println("rawGUID=" + myGUID.valueAfterMD5);
		//System.out.println("RandomGUID=" + myGUID.toString());
		String guid = myGUID.valueAfterMD5;
		if (guid == null) {
			return null;
		}
		else {
			return guid.toUpperCase();
		}
	}

    /*
     * Demonstraton and self test of class
     */
    public static void main(String args[]) {
	RandomGUID myGUID = new RandomGUID();
	System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
	System.out.println("rawGUID=" + myGUID.valueAfterMD5);
	System.out.println("RandomGUID=" + myGUID.toString());
	System.out.println("RandomGUID2=" + getGUID());

    }
}
